There are a variety of steam reforming processes such as steam methane reformers for production of syngas, steam reforming of lighter hydrocarbons, and steam reforming of lighter hydrocarbons to make hydrogen. In all of such steam reforming processes, a condensate, that is condensed from the product stream of the steam reformer, can be contaminated by a variety of compounds. This contamination can prevent exportation of steam made up of such condensate to customers that cannot tolerate such contaminants. Additionally, the condensate cannot be discharged as waste water without additional treatment.
For instance, in a typical steam methane reformer, natural gas consisting mostly of methane is reacted with excess steam at high temperature to produce a gas stream rich in hydrogen and carbon monoxide that is commonly referred to as syngas. The gas stream may be further processed to reduce the amount of carbon monoxide, thereby to produce more hydrogen. In the course of the process, the process gas, syngas, or hydrogen-rich gas, is cooled and excess steam is condensed out of the process gas. The resulting condensate, mostly water, is recovered and re-used to make steam by recovering heat in the steam methane reformer steam generating system. Steam is also produced from heat recovered when the combustion gas generated to heat the reformer is cooled to near ambient temperatures. Part of the steam from the steam methane reformer steam generating system may be exported and the remainder, referred to as process steam, is mixed with natural gas to produce syngas in the steam methane reformer. Typically, contaminants from the process condensate that end up in the export steam and the process steam include such compounds as carbon dioxide, methanol, ammonia, formic and acetic acid.
There have been a variety of prior art treatment schemes that have had as their aim the reuse of the contaminated process stream condensate. For instance, in United Kingdom Patent Application, GB 2006814A, water is condensed and separated from an intermediate syngas product. The resulting process condensate stream is pumped and heated with part of the superheated steam produced by a steam methane reformer to produce a heated water stream. The heated water stream is recirculated by a recirculation pump to a contacting column that is used to saturate an incoming hydrocarbon containing feed. The saturated hydrocarbon containing feed is combined with a remaining part of the make up steam and introduced into the steam methane reformer. In such manner, process condensate that contains contaminants is recycled.
In U.S. Pat. No. 4,193,776, a process stream condensate from a steam methane reformer is purified by stripping it with an incoming hydrocarbon containing feed stream before the use of such feed stream in the steam methane reformer. The purified process condensate is cooled and subjected to further purification, and used as makeup for the steam. The tower overhead is combined with the incoming hydrocarbon containing stream to be reformed.
The foregoing patents all involve some degree of expensive modification involving the provision of additional contacting columns, stripping columns and water treatment devices. As will become apparent, the present invention provides a process stream condensate recycle method that can be effectuated in a far less expensive manner than the prior art and that has special applicability as a retrofit to an existing plant.